The present invention relates to a horn speaker and more particularly relates to a horn speaker having a yoke whose pole piece is provided with a plurality of linear grooves in its front end.
A conventional loud speaker for use in a siren for a ship or the like, is required a type having a possibly larger voice output. In order to obtain this effect a powerful permanent magnet is used in a horn-type speaker to obtain a good electro-acoustic transducing efficiency, and a larger voice current is adapted to be input.
However, since a moving voice coil is positioned in a narrow air gap between a pole piece of a circular yoke and a permanent magnet or an annular yoke which supports the permanent magnet in order to obtain a strong magnetic field, its cooling effect is bad during the operation.
Accordingly, the temperature of the pole piece of the circular yoke may be remarkably raised, for instance, up to more than 130.degree. C., by the heat generated by the induced current of the moving coil vibrating and the heat of the moving coil itself. When the temperature of the pole piece is raised, the magnetic force is depressed, and thus the momentum of the moving coil is reduced. Consequently, the energy transform rate from the electric energy supplied in the form of the electric current into the kinetic energy is reduced, resulting in the increase of the heat generated of the moving coil.
Therefore, when an overinput is applied to the speaker or it is used continuously for a long period of time, the moving voice coil is often broken by overheat.